The present invention relates to pressure switches and more particularly to a pressure switch which mechanically detects the expansion and contraction of a conduit due to pressure changes of a fluid within said conduit.
In various applications it is desireable for certain elements such as pumps to be turned on or off according to the pressure within a conduit. Thus, there is a need to be able to measure the pressure within the conduit and to activate or deactivate an element in response to receipt of a sensed pressure. British Patent No. 284,679 discloses a pressure gauge using a tubular distendable element surrounded by a spring. As pressure increases within the tubular element, the element extends and the extension is shown by an indicator provided with markings. A similar arrangement is disclosed in U.S. Pat. No. 1,176,907. In that patent an expansion tube moves an extension viewable through an observation slot marked with gradiations. The higher pressures cause the tube to extend in length while lower pressures cause it to contract.
In U.S. Pat. No. 4,065,969 an apparatus is disclosed for detecting internal pressure of a fluid conduit including means for detecting lateral expansion and contraction of a thin-walled tubular element through compression of a piezo-conductive material placed between the thin-walled tubular member and an exterior rigid tube. Similarly, U.S. Pat. No. 4,090,404 detects the internal pressure within a conduit by clamping the conduit at two spaced locations and by employing detection means between the two clamped locations, the detection means being in the form of strain gauges which measure the lateral expansion of the conduit between the two clamped portions of the conduit.